JSON/MD5 problems

dub.json

{
    "name": "dansdedupe",
    "description": "one off script to rename and dedupe dans files",
    "authors": ["Alex Herrmann"],
    "targetType": "executable",
    "dependencies": {
      "std_data_json": "0.17.0"
    }
}

filedata.d

import std.stdio;
import std.container.rbtree;
import std.digest.md : md5Of, toHexString;
import std.datetime : DateTime, SysTime;
import std.parallelism;
import std.file;
// import std.json;
import stdx.data.json;
import std.range : chunks;
import std.array : array;
import std.algorithm : map;
import std.conv : parse;
import std.format : format;

public string str(in JSONValue injv) {
  return injv.toJSON();
}

public string toString(in JSONValue injv) {
  return injv.toJSON();
}

public string toPrettyString(in JSONValue injv) {
  return injv.toJSON();
}

void err(in string inst) {
  stderr.writeln(inst);
}

void log(in string inst) {
  stdout.writeln(inst);
}

struct filedata {
  DateTime modtime;
  string filename;
  ubyte[16] md5_hash;

  JSONValue fdToJson() {
    JSONValue[string] obj;

    auto outtime = JSONValue(modtime.date.toISOExtString());
    /*err("mtm: %s".format(outtime.toString()));*/
    obj["modtime"] = outtime;

    auto fname = JSONValue(filename);
    /*err("fnm: %s".format(fname.toString()));*/
    obj["filename"] = fname;

    auto outmd5 = JSONValue(cast(string) toHexString(md5_hash));
    /*err("md5: %s".format(outmd5.toString()));*/
    obj["md5"] = outmd5;

    auto jav = JSONValue(obj);

    err("tojson created:\n%s".format(jav.toString())); // works just fine here
    return jav;
  }
  unittest {
    filedata a;
    a.modtime = DateTime(1999,10,10);
    a.filename = "ayy";
    a.md5_hash = md5Of("lmao");

    auto json = a.fdToJson();

    log("Json: %s".format(json.toString())); // Not here though

    log("ran filedata tojson test");

  }
}

void main() {}

after replacing std.json with stdx.data.json;

Performing "unittest" build using dmd for x86_64.
taggedalgebraic 0.9.4: building configuration "library"...
std_data_json 0.17.0: building configuration "library"...
dansdedupe ~master: building configuration "application"...
Linking...
Running ./dansdedupe 
tojson created:
{
    "md5": "0F18FD4CF40BFB1DEC646807C7FA5522",
    "filename": "ayy",
    "modtime": "1999-10-10"
}
Json: {
    "md5": "�U���\u0000\u0000�U���\u0000\u0000�U���\u0000\u0000\u0017�N\u0000\u0000\u0000\u0000\u0000",
    "filename": "ayy",
    "modtime": "1999-10-10"
}
ran filedata tojson test